Frequency-reconfigurable multiple-input-multiple-output monopole antenna with wide-continuous tuning range

The design of a frequency-reconfigurable (FR) multiple-input-multiple-output (MIMO) monopole antenna with a wide-continuous tuning range in handheld devices is presented. The antenna consists of two symmetrical FR monopole elements and a FR defected-ground structure (DGS). The monopole elements have two sections, sections 1 and 2, connected together using a PIN diode. Section 1 alone generates a high-frequency band at 2.26 GHz. By turning ON the PIN diode, sections 1 and 2 will be connected together to generate a low-frequency band at 1.93 GHz. The DGS is used to achieve high isolation between the monopole elements and reconfigurable to follow the low- or high-frequency operations. Simple and novel biasing circuits employing only 3 DC wires are designed to control these diodes. The methodology of using the design in other frequency bands is proposed. Results on S-parameters, radiation pattern, realized peak gain and envelope-correlation coefficient (ECC) are presented. Measured results show that the antenna has a wide-frequency tuning range from 1.88 to 2.64 GHz, covering the long-term-resolution (LTE) 1, 2, 23, 25, 33-37 and 39-40 bands with low mutual coupling and ECC of less than -20 dB and 0.5, respectively. The effects of the feeding cable used in measurement are studied.